Virginia has state mandated inspection for all trailers with brakes and my trailer needed a new inspection. Everything worked when I left the house but when I got to the inspection station the running lights were out. Dang. . . Checked the trailer plug and it was obvious one connector on the plug was bad. Changed the plug out and thought I had mixed up the wires. Changed wires around, rinse and repeat.
Finally got the bright idea to hook up to a second trailer- same thing. Ok, maybe the truck plug was bad. I had another one and had been meaning to swap it anyway. Made the swap which wasn't bad except of course getting dirt in my face and around my eyes- glasses stopped most of it. Go back to the trailer and. . . . nope. WTF? I've got turn signals, brake lights and trailer brakes but no running lights but only 4.5 volts on the running lights connector. Finally my rather dim bulb brightened up a bit and I swapped out the fuse on the truck- all is good.
I could have fixed the issue in 15 seconds but the fuse showed almost no resistance when out but evidently was doing something flaky when installed.
Somebody else can kick my butt for a while, my legs are getting tired of doing it myself. Check the simple stuff first, dummy! I did check resistance but didn't actually change it until the very end of the process.